1. Field of the Invention.
Removal or separation of suspended tar and solid particles from a coal liquefaction stream is a problem common in the developing coals-to-liquids industry. In the production of synthetic liquid coal products, coal is normally crushed, mixed with a solvent to form a "slurry" and upgraded by hydrogenation to produce coal liquefaction products, "entrained" solid particles, tar and the like. Typical solutions to this problem involve distillation, evaporation, filtration, settling and centrifugation to remove the solids. The most common method of separation is distillation or filtration. It is possible to distill or evaporate any volatile liquid away from less volatile liquids and non-volatile solids; however, the cost for heat and energy in this process may be commercially prohibitive from a practical viewpoint. In addition, the solids which are in the boiling fraction are quite high in surface area and are believed to have strong adsorptive capacity for liquids. Therefore complete liquid removal from the solids, both ash and unconverted coal, is difficult, also some liquid material must be left in the solids phase to maintain fluidity of the bottoms to permit the bottoms to flow out of the vacuum flash or vacuum distillation unit of a typical solids separation process.
It has now been discovered that tar and solids can readily be separated from coal liquefaction products, utilizing a minimum amount of energy, by mixing said products with a halogenated aliphatic solvent to form two phases, one (the upper) phase containing said tar and/or solids and the other (the lower) phase containing said solvent and the remainder of said coal liquefaction products. Absorbed solvent is readily recovered from the tar and solids and the tar and solids-free, coal liquefaction product using a minimum amount of energy because of its stability and low boiling point. After the separation step, the solvent can readily be recycled to recover additional tar and solids in a continuous separation process.
2. Brief Description of The Prior Art
The separation of dispersed solids from organic liquids is known and appreciated in the prior art. For example, in the conversion and upgrading of solid carbonaceous materials (i.e. coal, etc.) into liquid hydrocarbons, tremendous quantities of the hydrocarbons are produced which contain unreacted coal, ash particles and the like. One method of removing dispersed solids from organic liquids, for example hydrocarbons, is disclosed in U.S. Pat. No. 3,563,885, entitled Removal of Dispersed Solids From a Liquid, issued to Talbot, on Feb. 16, 1971. The reference relates to the removal of dispersed solids from organic liquids by adding a small quantity of ultra high molecular weight polyethylene, under agitation and at elevated temperature, to the liquid. The mixture is allowed to cool until the polyethylene containing the dispersed solids coagulates. The coagulated material is next removed by conventional techniques.
Another approach for separating liquid hydrocarbons from mineral solids is set forth in U.S. Pat. No. 3,941,679, entitled Separation of Hydrocarbonaceous Substances From Mineral Solids, issued to Smith et al, on Mar. 2, 1976, which discloses a method for separating liquid hydrocarbons from the mineral solids of tar sands, oil shales and similar geological composites. In particular, liquid trichlorofluoromethane is used to dissolve and extract the hydrocarbons from the mineral solids.